The Diagenesis of Sandstone in the Sixth Oil Layer of the Upper Triassic Yanchang Formation in Baibao Area, Ordos Basin

The properties of the reservoir sandstone mainly depend on the sedimentary environment and the diagenesis. The thoroughly research on the diagenesis of the sandstone reservoir in the sixth oil layer of the Upper Triassic Yanchang formation has been one of the core geological problems. The comprehensive analysis shows that the reservoir rock types are mainly fine-grained-powder fine-grained feldspar lithic sandstones and lithic arkoses; rocks have low compositional maturity and medium textural maturity. Sandstone generally experienced strong compaction transformation, mainly mechanical compaction, making the primary pores in sandstones significantly loss. Feldspar etc. often occurs apparent dissolution, and secondary pores widely developed. In addition, the sandstones also experienced late cementation and fracturing. The sandstone reservoirs are in the middle diagenetic stage B period.